Ceramic dielectrics



, p 1969 SHINOBU FUJIWARA ETAL 3,440,067

CERAMIC DIELECTRICS Sheet Filed June 8, 1964 DIELECTRIC CONSTANT() L02 0s-2Ti O2 Molar Q-VALUES Molar LazOa-2Tl O2 aw div/Wm.

INVENTORS April 1969 SHINOBU FUJIWARA ETAL 3,440,067

cmmuc nmmcwnxcs Filed June a, 1964 Sheet 3 of 2 Molar au-M INVENTORS United States Patent 3,440,067 CERAMIC DIELECTRICS Shinobu Fujiwara, Minami-Akita-gun, Akita-ken, and

Takao Shiraiwa, Akita-shi, Japan, assignors to TDK Electronics Co., Ltd., Tokyo, Japan Filed June 8, 1964, Ser. No. 373,314 Int. Cl. C04b 35/00 US. Cl. 106-39 4 Claims ABSTRACT OF THE DISCLOSURE Ceramic dielectric materials are provided having a relatively large dielectric constant and high Q-value, namely, low dielectric loss. The dielectric materials consist essentially of a sintered mixture of BaTiO ranging from 30 to 93 molar percent, La O -2TiO ranging from 1 to 30 molar percent and SrTiO ranging from 1 to 69 molar percent.

The present invention relates to an improvement in ceramic dielectrics.

The object of this invention is to provide ceramic dielectrics which have relatively large dielectric constant and high Q-value, namely, low dielectric loss.

Recently, the frequently range used for communication equipments is being developed toward the higher frequency region. With the increase of thefrequency, the electrostatic capacities of condensers may be small and therefore the dielectric constants need not be extremely large. On the other hand, the Q-values of condensers require high values because a large loss coefiicient of condensers severely impairs the utility at high frequency. The dielectrics in accordance with this invention have the extremely suitable properties for the above-mentioned purpose.

The ceramic dielectrics, which have been widely used, may be roughly classified into two types; the one mainly comprises titanium oxide and the other mainly comprises barium titanate.

Titanium oxide type dielectrics which have been widely used as temperature compensators, have high Q-values ranging from 2000 to 3000 at high frequency, whereas their dielectric constants are small. For example, the dielectric constant of rutile type ceramics which are regarded as relatively highly practical type, is only of the order of 114 or so.

On the other hand, barium titanate type dielectrics have large dielectric constants of more than 2000, and low Q-values of about 150, with extremely large temperature dependence of dielectric constant, and the minimum value of the temperature coefiicient of dielectric constant is approximately --6000 10- C.

The characteristic feature of the present invention is to provide a type of ceramic dielectrics which lies between those of the two types mentioned above. It has larger dielectric constants than those of the titanium oxide type which have small dielectric constants, and much higher Q-values than those of barium titanate type which have large dielectric constants.

In detail, this invention relates to a type of ceramic dielectrics whose main components are barium titanate (BaTiO lanthanum (III) titanium (IV) oxide and strontium titanate (SrTiO and it has dielectric constants ranging from 100 to 1400 or so, Q-values ranging from 600 to 15,000 and temperature coefiicients of dielectric constants ranging from -100 l0 C. to -7000 l0- C. or so.

In the present invention, the range of the proportions of the three components, where the favorable properties 3,440,067 Patented Apr. 22, 1969 of medium dielectric constant, low dielectric loss and small temperature coefiicient of dielectric constants can be obtamed, is limited, as follows:

Molar percentage BaTiO 30-93 L320}; 1-3 0 SrTiO 1-69 The reasons for limiting the proportions to the said values are: (1) When the proportion of barium titanate (BaTiO is below 30 molar percent, dielectric constant (6) becomes small and when it exceeds 93 molar percent, Q-value becomes extremely low. (2) When the proportion of lanthanum titanium oxide (La O -2TiO is below 1 molar percent, the effect of addition thereof is ineffective, and when it exceeds 30 molar percent, vitrification is difficult. (3) When the proportion of strontium titanate (SrTiO is below 1 molar percent, the desired characteristics can not be obtained, and when it exceeds 70 molar percent, dielectric constant (6) becomes small.

For a better understanding of the present invention, reference is had to the accompanying drawings.

In the accompanying drawings:

FIGURE 1 is a ternary diagram representing the range of the proportion of the three components of the ceramic bodies within the present invention, that is, barium titanate (BaTiO lanthanum titanium oxide (La O -2TiO and strontium titanate (SrTiO The numerical values and the curves in the diagram represent the dielectric constants.

FIGURE 2 is a ternary diagram representing the range of the proportion of the three components of the ceramic bodies within the present invention, that is, barium titanate (BaTiO lanthanum titanium oxide (La O -2TiO and strontium titanate (SrTiO The numerical values in the diagram represent the Q-values.

FIGURE 3 is a ternary diagram representing the range of the proportion of the three components of the ceramic bodies within the present invention, that is, barium titanate (BaTiO lanthanum titanium oxide (La O -2TiO and strontium titanate (SrTiO The numerical values and the curves in the diagram represent the temperature coefficients of dielectric constants. The measurements of the properties have been all carried out at a frequency of 1 megacycle per second.

The dielectrics of the present invention are produced by the following procedure:

Stir raw materials, that is, barium carbonate (BaCO strontium carbonate (SrCO lanthanum oxide (La O and titanium oxide (TiO for a period enough to render the mixture homogeneous, calcine the mixture in oxidizing atmosphere at the temperature range of 1100" C. to 1300 C. for about 2 hours, pulverize the calcined material into fine powder followed by adding a binder in solid or liquid form, in which the materials are not soluble, and form the powder into the desired shape such as disc under sulficient pressure for shaping, and then sinter finally the shaped materials in oxidizing atmosphere at the temperature range of 1300 C. to 1400 C. for about 3 hours.

The following examples will give a closer insight into the present invention.

EXAMPLE I The raw materials employed were barium carbonate (BaCO strontium carbonate (SrCO lanthanum oxide (La O and titanium oxide (TiO In this case, barium titanate (BaTiO can be formed by the reaction of a mixture of barium carbonate (BaCO with titanium oxide (TiO on firing, strontium titanate (SrTiO can be formed by the reaction of a mixture of strontium carbonate (SrCO with titanium oxide (TiO on firing and lanthanum titanium oxide (La O -2TiO can be formed by the reaction of a mixture of lanthanum oxide (La O 3 with titanium oxide (TiO on firing. The titanium oxide (TiO barium carbonate (BaCO strontium carbonate (SrCO and lanthanum oxide (La O were added so that the following proportion was finally given:

BaTiO :La O -2TiO :SrTiO =7 7 18 (molar percent) Then the mixture was mixed and stirred for about twenty hours. The calcination of raw material in powder mixture was carried out in air at the temperature of 1260 C.

After calcination, the material was pulverized into a fine powder so that the coarsest particles would pass a 250 mesh screen and the finest particles would not pass a 300 mesh screen. To the material in powder form, a small quantity of wheat starch solution in water was added. The material was shaped and pressed into disc shape of 15.2 millimeters in diameter and 0.8 millimeter in thickness under the shaping pressure of four tons per square centimeter, and then sintered finally in air at a temperature of 1350 C. for three hours.

The characteristics of ceramic dielectric thus obtained show following values:

dielectric constant (E)732, Q-valuel3644, temperature coefiicient of dielectric constant- EXAMPLE II The raw materials employed were barium carbonate (BaCO strontium carbonate (SrCO lanthanum oxide (La o and titanium oxide (TiO In this case, too, barium titanate (BaTiO strontium titanate (SrTiO and lanthanum titanium oxide (La O -2TiO can be formed on firing as in Example I. The titanium oxide (TiO barium carbonate (BaCO strontium carbonate (SrCo and lanthanum oxide (La O were added so that the following proportion was finally given:

BaTiO :La O 2TiO :SrTiO =87: :3 (molar percent) Then the mixture was mixed and stirred for about twenty hours. The calcination of raw material in powder mixture was carried out in air at a temperature of 1280 C.

After calcination, the material was pulverized into a fine powder so that the coarsest particles would pass a 250 mesh screen and the finest particles would not pass a 300 mesh screen. To the material in powder form, a small quantity of wheat starch solution in water was added. The material was shaped and pressed into disc shape of 15.2 millimeters in diameter and 0.8 millimeter in thickness under the shaping pressure of four tons per square centimeter, and then sintered finally in air at a temperature of 1370 C. for three hours.

4 The ceramic dielectric thus obtained shows following characteristics dielectric constant (e)-415, Q-value--5605, temperature coefficient of dielectric constant- What is claimed is:

1. A ceramic dielectric consisting essentially of a sintered mixture of BaTiO ranging from 30 to 93 molar percent, La O -2TiO ranging from 1 to 30 molar percent and SrTiO ranging from 1 to 69 molar percent.

2. A ceramic dielectric according to claim 1 in which the proportion of BaTiO is from about 77 to about 87 molar percent, the proportion of La O -2TiO is from about 5 to about 10 molar percent, and the proportion of SrTiO is from about 3 to about 18 molar percent.

3. A ceramic dielectric material in accordance with claim 1 wherein the proportion of BaTiO is about 77 molar percent, the proportion of La O -2TiO is about 5 molar percent and the proportion of SrTiO is about 18 molar percent.

4. A ceramic dielectric material in accordance with claim 1 wherein the proportion of BaTiO is about 87 molar percent, the proportion of La O -2TiO is about 10 molar percent and the proportion of SrTiO is about 3 molar percent.

References Cited UNITED STATES PATENTS 2,985,700 5/1961 Johnston 10639 3,268,783 8/1966 Saburi 317--258 FOREIGN PATENTS 574,577 1/ 1946 Great Britain.

OTHER REFERENCES MacChesney et al.: Stabilized Barium Titanate Ceramics for Capacitor Dielectrics, J. Am Ceramic Soc., volume 46 (pp. 19'7-202), May 21, 1963.

Kainz: Dielectric Properties of the Systems Barium- Strontium-Lanthanum T itanate, Ceramic Abstracts, October 1958 (p. 277, Item D).

Kainz II: Ber. deut. Keram. Ges., 35 [3], pp. 69-77 (1958).

Marzullo et al.: Dielectric Properties of Titania or Tin Oxide Containing Varying Proportions of Rare Earth Oxides, J., Am. Cer. Soc, vol. 41, January 1958, PP. 40-41.

HELEN M. MCCARTHY, Primary Examiner.

US. Cl. X.R. 317-258 

